The invention relates to a semiconductor component with a circuit configuration for driving an electrical load, with a control circuit having at least one power switch and a drive configuration, which drives the at least one power switch and via which current is supplied to the load. Furthermore, the circuit configuration has a temperature evaluation circuit which is intended to protect the control circuit and/or the load against overheating.
Power switches which are used to switch loads, e.g. DC motors, asynchronous motors or the like, must have protection against short circuits in the load circuit. This is necessary because otherwise the power switch or, in the worst case, even the load could be destroyed.
For this purpose, the power switches are provided, for example, with one or more temperature sensors whose signals are evaluated by an evaluation circuit. The power switch is switched off upon the occurrence of a short circuit that results in a substantial temperature increase in the power switch. If a specific temperature value is exceeded, the power switch is switched off and destruction is consequently prevented.
The publication xe2x80x9cSmart Power ICs, Technologies and Applications,xe2x80x9d Morari, Bertotti, Vignola (Eds.), Springer Verlag 1996, p. 85ff., describes power switches which have a sensor for their protection. For this purpose, a sensor chip is bonded on the semiconductor chip of the power switch. The sensor chip is electrically connected to the power switch. The connection is effected between the gate electrode of the power switch and the source electrode. The sensor chip is thereby designed as a thyristor which responds at a predetermined temperature of 150xc2x0 C. and switches off the power switch when this temperature limit is exceeded. Consequently, the sensor chip is connected to the power switch in a readily thermally conductive manner.
Furthermore, power switches are known in which a diode or a transistor sensor is integrated in the vicinity of the hottest location in the power switch. The signal of the sensor is then processed by an evaluation circuit in such a way that the power switch is switched off or at the very least power reduction is effected as soon as the temperature at the sensor exceeds a predetermined threshold. The switching thresholds normally lie between 150xc2x0 C. and 180xc2x0 C.
Despite close thermal coupling between the power switch and the sensor, the actual temperature present at the power switch is present somewhat later at the sensor on account of thermal inertia. This means that the sensor reacts in a somewhat delayed manner. This temporal, delayed response of the sensor is all the more pronounced the lower the temperatures of the housing surrounding the semiconductor component are. It is possible, therefore, for the semiconductor component to be destroyed at low housing temperatures e.g. in the event of a high short-circuit power, while at higher housing temperatures the sensor can still switch off the power switch in good time or reduce the power. The housing temperature is greatly influenced by the ambient temperature.
It is accordingly an object of the invention to provide a semiconductor component with a circuit configuration for switching an electrical load, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which affords improved protection against destruction.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor component with a circuit configuration for driving an electrical load, comprising a control circuit with at least one power switch connected to an electrical load for supplying current to the electrical load and having a drive configuration connected to and driving the power switch. The semiconductor component having a first temperature detector thermally closely coupled to the power switch and outputting a first temperature signal representing a temperature at the power switch and a second temperature detector outputting a second temperature signal. A temperature evaluation circuit is connected to the first and second temperature detectors and to the drive configuration for generating an output signal from the first and second temperature signals and feeding the output signal to the drive configuration.
In accordance with an added feature of the invention, the second temperature detector is disposed to sense an ambient temperature and the second temperature signal is dependent on surroundings of the semiconductor component.
In accordance with an additional feature of the invention, a housing encloses the control circuit and the second signal depends on a housing temperature.
In accordance with another feature of the invention, a lead frame carries the circuit configuration, and the second temperature detector supplies the second temperature signal dependent on a lead frame temperature.
In other words, the invention proposes a semiconductor component having a circuit configuration for driving an electrical load, with a control circuit comprising at least one power switch with a drive configuration. A current can be fed to the load via said control circuit. Furthermore, the semiconductor component has at least one temperature detector, which is thermally closely coupled to the power switch, and also a temperature evaluation circuit, which controls the power switch in a manner dependent on the signal of the thermally closely coupled temperature detector. The concept on which the invention is based consists in the semiconductor component having a further temperature detector, in which case the temperature evaluation circuit generates an output signal, which is dependent on the temperature of the thermally closely coupled temperature detector and the further temperature detector, and feeds said signal to the drive configuration.
The temperature sensor of the first temperature detector which is thermally closely coupled to the power switch may be, for example, a thyristor, a flip-flop or any other desired logic circuit. The temperature detector which is thermally closely coupled to the power switch may in this case be designed as a separate semiconductor chip which is applied to the power switch via an insulating layer having good thermal conductivity. However, it is also conceivable for the temperature detector which is thermally closely coupled to the power switch and the power switch to be monolithically integrated. The advantage consists in the fact that the power switch and the temperature detector can be produced in a single fabrication stage and optimum emplacement of the temperature detector in the power switch is possible.
The further temperature detector of the invention generates a signal which is dependent on the surroundings and is supplied to the temperature evaluation circuit. The effect achieved as a result of this is that the ambient temperature, which influences the point in time at which the drive configuration responds, can concomitantly be taken into account. In another refinement, the further temperature detector supplies a signal which is dependent on the housing temperature. In a further refinement, the further temperature detector supplies a signal which is dependent on the lead frame temperature. The effect whereby the surroundings of the semiconductor component are taken into account is achieved as a result of these refinements, too.
If the semiconductor component is operated in very cold surroundings, then the housing or lead frame temperature is likewise low. This low temperature affects the temperature detector which is thermally closely coupled to the power switch. If a short circuit occurs in the load circuit, then the power switch is heated very rapidly. Since the temperature detector which is thermally closely coupled to the power switch follows the heating of the power switch with a degree of inertia, this delay time is prolonged by the low housing temperature. Damage to the power switch or even to the load could occur. On account of the further temperature detector which takes account of the ambient temperature or the housing/lead frame temperature, the temperature threshold in the temperature evaluation circuit is influenced in such a way that in the case of a low signal value of the further temperature detector, the power switch is switched off or has its power reduced at a lower temperature of the temperature detector which is thermally closely coupled to the power switch. If, on the other hand, the semiconductor component is operated at a high ambient temperature, then the temperature detector which is thermally closely coupled to the power switch can respond more rapidly, and the power switch can thus be switched off at a higher temperature threshold.
In accordance with a further feature of the invention, the second temperature signal assumes temperature values including a first signal value and a second signal value, and the drive configuration is adapted to control the power switch in dependence on the second temperature signal such that a first switching threshold is critical up to the first signal value and a second switching threshold is critical above the second signal value, wherein the first switching threshold is lower than the second switching threshold.
In other words, the semiconductor component is set up so that the drive configuration controls the power switch in dependence on the signal of the second temperature detector in such a way that a first switching threshold is critical up to a first signal value and that a second switching threshold is critical above a second signal value. In this case, the first switching threshold is smaller than the second switching threshold. This means nothing more than that the drive configuration controls the power switch in such a way that, depending on the further temperature detector (e.g. ambient temperature), in the case of a low signal value the switch-off threshold assumes a low value, whereas, in the case of a high signal value of the further temperature detector, the power switch is switched off only at a higher value of the temperature detector which is thermally closely coupled to the power switch.
In accordance with again an added feature of the invention, the first signal value is less than the second signal value, or in the alternative, it is equal to the second signal value.
In the first embodiment, the first signal value is in this case less than the second signal value. This means that if the semiconductor component is operated at a low temperature determined by the further temperature detector, up to a first signal value the power switch is switched off at a low switching threshold (temperature of the temperature detector which is thermally closely coupled to the power switch). If the temperature of the further temperature detector exceeds this first signal value, then the switching threshold is moved upward linearly with the increase in this temperature signal. When a second signal value is reached, which is greater than the first signal value (a greater temperature than the temperature of the first signal value), the power switch is switched off at a second switching threshold, which is higher than the first switching threshold.
In the second embodiment, the first signal value is equal to the second signal value. This means that until a specific limit temperature of the further temperature detector is reached, the power switch is switched off at a low switching threshold, so that it is then switched off at a second higher switching threshold of the temperature detector which is thermally closely coupled to the power switch when the first signal value is exceeded.
The advantage of operating the power switch in a manner dependent on a temperature signal which is closely coupled to the power switch and at the same time on a further temperature signal which takes account of the external ambient influences on the power switch consists in the fact that the short-circuit strength is ensured even at cold ambient temperatures. At the same time, however, it is ensured that the semiconductor component functions fully even at high ambient temperatures. The power switch and the load operated by it thus have improved endurance to withstand failure.
In accordance with a concomitant feature of the invention power switch and the first temperature detector are monolithically integrated. Also, the drive configuration and the evaluation circuit may be monolithically integrated.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor component with a circuit for driving an electrical load, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.